System and method of control.



R. E. HELLMUND.

SYSTEM AND METHOD OF CONTROL.

APPLICATXON FILED JAN. 7. i914. 1,278,923. Patent-ed Sept. 17,1918.

2 SHEETSSHEET I.

INVENTOR WlTNESSES: 5W]

I I ATTORIQEVY R. E. HELLMUND. SYSTEM AND METHOD OF CONTROL.

APPLICAUON FILED JAN-7,1914- Patented Sept. 17, 1918.

2 SHEETSSHEET 2.

WITNESSES:

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UNITED STATES RUDOLF E. HELLMUND, OF PITTSBURGH HOUSE ELECTRIC AND MANUFACTUB SYLVANIA.

ING COMPANY, A CORPORATION OF PENN- SYSTEM AND METHOD OF CONTROL.

Application filed J anuary 7, 1914. Serial No. 810,764.

'1 0 all whom it may concern:

Be it known that I, RUDOLF E. HELL- MUND, a subject of the German Empire, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Systems and Methods of Control, of which the following is a specification.

My invention relates to systems and methods of control, and it has special reference to the control of alternating current motors of the commutator type or similar machines, whereby good con'nnutating and general op erating conditions are obtained, particularly during the starting period.

The object of my invention is to provide a sytem and method of control of the aboveindicated character which shall be reliable and effective in operation and which shall involve relatively simple apparatus.

The motor I prefer to employ in carrying out my invention comprises a suitable armature, an exciting or torque-producing field winding and a compensating or inducing winding having more turns than the armature winding, preferably approximately twice as many.

At starting, a temporarily weakened field flux in the motor is desirable in order to obtain the high armature current required to produce a satisfactory starting torque without causing undue sparking at the brushes by reason of excessive transftn'mcr action in the coils shortcircuited by the brushes, as would be the case with a heavy field flux. However, the weakened field should be of only temporary duration or the motor will tend to run at an excessive speed.

i'lccording to my invention, I provide a method of control whereby the motor is doubly-fed from a suitable source throughout the range of operation. The

weakened field flux at starting is secured by comiectmg the exclting winding and the compensating winding in series and later changing over to a series connection of the exciting winding and the armature in order to obtain the stronger field flux desired during operation. In this case, it will be noted that the current in the compensating field winding approximates one-half the value of the'armature current by reason of the mulual transformer action, in View of the ratio of turns in the respective windings. As a method for maintaining good commutating conditions during the change-over above mentioned, I first insert a suitable resistoracross the compensating winding, accomplish the change-over, and then disconnect the resistor, as will hereinafter be more fully explained.

For starting the motor from the customary transformer winding, I prefer to connect the motor, as a whole, across a predetermined portion of the winding, and the inner armature terminal to an outer point thereof. Such an arrangement is employed in view of the following theoretical considerations.

If the motor is connected as a straight repulsion motor, that is, if the armature is directly short-circuited during the starting period, the armature Will tend to attain a speed corresponding to the theoretical synchronous speed of the machine. If the inner. armature terminal is connected to a point intermediatethe point of connection of the motor, terminals, then the armature will tend to revolve at a speed higher than synchronism, while, if the said inner terminal is connected to a point outside the portion of the transformer winding across which the motor, as a whole, is connected, the armature will. run at a speed less than its synchronous speed. i I

The last-named connection is, therefore, preferable for starting, and, as the speed and counter-'electromotive force of the machine increase, the point of connection .to the transformer winding of the inner armature terminal may be varied, if desired,

through the short-circuit position to the position of over-s'ynchronism.

It might appear that when the inner terminal is connected to a point outside the normal motor terminals, that the direction of current flow through the armature would be reversed with respect to the main field and that the direction of rotation would be reversed. It is found, however, that when the connections are made in this manner for starting that the inducing or commutating Winding induces a higher electromotive force in the armature winding than the trans former voltage across the terminals thereof and accordingly the armature may be said to PATENT OFFICE.

, PENNSYLVANIA, ASSIGNOR TO WESTING- sutficient current therein to supply the necessary torque and when the inner terminal of the armature is connected between the normal terminals of the motor for over synchronous speeds, a portion of the armature current flows thereinto through the brushes and the remainder is induced therein by the inducing winding.

In the accompanying drawing, Figures 1 to 7, inclusive, are diagrammatic views of a series of connections employed in a control system arranged in accordance with my invention; and Fig. 8 is a switch sequence chart therefor.

Referring to the drawing, an auto-transformer 1 or other suitable source of alternating current supplies energy to a suitable motor having an armature winding 2', an exciting or torque-producing winding 3 and a compensating or inducing winding 4 of approximately twice the number of turns of the armature winding 2, through a plurality of separate and suitable switches 5 to 8, inclusive. A suitable resistor 9 maybe connected across the compensating winding l by means of a switch 10. The resistor 9 preferably has an impedance of such a value that the connection thereof in parallel with the winding 4 will cause a reduction of the current therein to approximately one-half the immediately preceding value.

Assuming that the connections are as shown in Fig. 1 of the drawing, the switches all being open, and that the autotransformer 1 is suitably energized, the operation of the system is as follows: v

Switches 5, 7 and 8 are first closed, thereby connecting the armature winding 2 across a suitable relatively small portion of the auto-transformer 1, and connecting the two field windings in series relation across the same and another portion, as shown in Fig. 2. The motor is thus doubly fed at starting.

It will be noted that the inner armature terminal 11 is connected by a conductor 19. to an outer point 13 of the transformer winding; that is, to a point outside of that portion of the winding across which the motor, as a whole. is connected. If desired, the conductor 12 may then be moved along the t 'ansformer winding to the armature short-circuiting position, which effect may be obtained by opening the switch 7 and closing the switch 7*, as shown in Fig. 3. Over svnchronous speed may then be obtained by opening the switch 7* and closing the switch 7, asshown in Fig. 4. While in many cases these accelerating positions are not necessary, I find that they are desirable in order to obtain a smooth and comfortable increase in speed, especially when the motor is employed for driving railway vehicles.

In order to obtain the next higher speed a changeover may be made whereby the exciting winding 3 is placed in series with the armature winding '2. This change-over involves the opening of switch 7 and the closing of switch 6. However, if the switch 6 should be closed before the switch 7 is opened, the changed circuit conditions would cause the current in the exciting winding and consequently, the field flux produced thereby to lag substantially 90 in phase behind the armature current, and the motor torque would thereupon disappear. On the other hand, if the switch 7"should be opened before the switch 6 is closed, a series circuit of all the motor windings is formed. The current in the compensating field winding would for an instant equal the armature current, and, by reason of the relatively large number of turns in the field winding, would set up a very strong field flux of an undesirable phase relation, thereby causing sparking and other bad commutating conditions.

In order to obviate the above diiiicultics, the resistor 9 is employed to advantage. In changing over, switch 10 is first closed, giv ing the connections of Fig. 5-; then switch 7 is opened and switch 6 is closed, as shown in Fig. 6; and last of all the switch 10 is opened as indicated in Fig. 7. In this way, the resistor 9 divides the doubled current in the compensating winding circuit that ensues upon the momentary connection of all the motor windings in series, about equally with the compensating field wind-' ing and thus maintains the field flux thereof at approxin'lately its pro-per value to insure good commutating conditions.

For subsequently increasing the motor speed, any suitable method may be employed, such as shifting in position one or more of the motor connections to the auto-transformer 1 that are shown in the drawing. Preferably, the connection through the switch 6 is shifted to impress increasing voltages upon the armature winding 2.

Fig. 8 illustrates the sequence of switch operation, whereby the above results are attained in a simple manner.

I do not wish to be restricted to the particular arrangement of connections herein set forth, but desire that only such limitations shall be imposed as are indi 'ated in the appended claims.

I claim as my invention:

1. The method of operating an alternating-eurrentmotor of the compensated commutator type wherein the main and compensating field windings and. the armature winding are connected in series relation that consists in connecting the series circuit and said armature winding to predetermined portions of a source of alternating current, temporarily reducing the current in one of said windings, opening one of the motor armature connections and connecting a point intermediate the windings to a predetermined point of said source.

2. The method of operating an alternating current motor of the compensated commutator type, wherein the main andcompensating field windings are connected in series with the armature. winding, that consists in connecting the terminals of the motor across a predetermined portion of a source of alternating current and an intermediate point in said motor to a predetermined point of said source, temporarily reducing the current in one of said windings, opening connection between said points, and connecting a second intermediate point in said motor to asccond predetermined point of said source.

3. The method of operating an alternating current motor of the compensated commutator type, wherein the main and compensating field windings are connected in series with the armature winding, from a transformer winding that consists in connecting the terminals of the motor across said transformer winding and one terminal of the motor armature to a predetermined point of said transformer winding, temporarily reducing the current in one of said field Windings, opening the intermediate motor connection, connecting a point intermediate the fieldwindings to a second predetermined point of said transformer winding, and

varying the impressed voltages to increase the motor speed.

4. The method of operating an alternating current motor of the compensated commutator type wherein the main and compensating field windings are connected in series relation with the armature winding, that consists in connecting the terminals of the motor across a predetermined portion of a source of alternating current and an intermediate point in said motor to a predetermined point of said source, inserting a trans lat-ing device of predetermined impedance in parallel with one of said windings, opening the connection between said points, connecting a second intermediate point in said motor to an intermediate point of said source, and excluding said device.

The method of operating an alternating current motor of the commutator type from a transformer winding that consists in connecting the terminals of the motor across a predetermined portion of transformer winding and one terminal of the motor armature to a predetermined point of said transformer winding, inserting a-translating device having an impedance substantially equal to that of one of said field windings across nection, connecting a point intermediate the field windings to an intern'iediate point of said transformer winding, and excluding said device. I

a 6. The combination with an alternatingcurrent motor of the commutator type having a plurality of field windings connected in series circuit, of a transformer winding, means for initially connecting different portions of said transformer winding to said series circuit and to the armature winding of said motor, a translating device, means for inserting said device across at least a portion of one of said motor windings, means for connecting an intermediate point in said field windings to a predetermined point in said transformer, and means for rendering said device ineffective.

7. The combination with an alternating current motor of the commutator type having a plurality of field windings connected in series circuit, of a transformer winding, switching means for initially connecting different portions of said transformer winding to said series circuit and to the armature winding of said motor, an impedance device, switching means for connecting said device across one of said windings, switching means for connecting a point intermediate the field windings to a predetermined point in said transformer winding, and means for excluding said device from the circuit.

8. The combination with an alternating current motor of the commutator type provided with an exciting winding and an inducing winding on the .stator having a larger number of turns than the armature winding, of a transformer winding, switch ing means for initially connecting different portions of said transformer winding to the field windings disposed in series and to the armature winding, a translating device having an impedance substantially equal to that of said inducing winding, switchingmeans for connecting said device across the inducing winding, switching means for connecting a point intermediate the field windings to an intermediate point insaid transformer winding, and means for eliminating said resistor. v

9. The method of operating an alternating current motor of the compensated commutator, type wherein the main and compensating field windings are connected in series relation that consists in severally connecting certain sets of the motor windings to separate portions of a transformer at starting, applying a certain voltage across all of said sets of windings in series relation, and connecting a point in the field winding circuit to a point on said transformer of intermediate voltage value. 10. The method of operating an alternating current motor of the compensated commutator type wherein the main and compensating field windings are connected in series relation and having a greater number of turns in its compensating field winding than in its armature winding that consists in severally connecting certain sets of the motor windings to separate portions of a source of alternating current at starting, applying a certain voltage across all of said sets of windings in series relation, and connecting a point in the-field winding circuit to a point of intermediate voltage value.

11. The method of accelerating an alternating-current commutator motor having an inducing winding and an armature winding, said inducing winding embodying substan tially twice the turns of said armature winding, which consists in connecting the motor terminals across a source of alternating current, and connecting a point of the motor circuit common to the armature and field windings to a point of said source, adjusting the connection to said common point to produce an electromotive' force in said armature from said inducing winding which shall be greater than the back electromotive force of said armature Whereby electrical energy is supplied from said armature to said current source, short-circuiting said armature so that all the energy induced therein by said inducing winding shall be consumed in said winding, and then supplying a portion of the electromotive force of the armature by in duction from: said inducing winding and the remainder by conduction from saidsource.

12. The combination with an alternatingcurrent commutator motor having an armature winding and an exciting and inducing field winding, said inducing winding embodying substantially twice as many turns as said armature winding, of a transformer, the terminals of said motor being connected across a portion of said transformer winding, and an intermediate point in the motor circuit common to said armature and said field winding being connected to a pointoutside of the main motor connections, said connection inducing more electrical energy in said armature winding than is consumed by said armature, a certain portion of said energy being returned to said transformer.

13. The method of accelerating an alternating current motor of the commutating type provided with an inducing Winding which comprises connecting the inducing and exciting windings in series relation across a relatively large portion of the source and connecting the armature across a rel atively small portion of the source and there after connecting the inducing winding across a portion of the source and connecting the armature and exciting winding in series relation across such a portion of the source that the current in the exciting winding is relatively g eater for the samenrmature load current than with the preceding connection and the voltage impressed acrossthe armature is reversed relative to the preceding connection. a

l t. The method 0t accelerating an alter: nating current motor of thecommutating type provided with an inducing winding having a greater number of turns than the armature which comprises connecting the inducing and exciting windings in series relation across a relatively large portion of the source and connecting the armature across a relatively small portion of the source and thereafter connecting the inducing wind-ing across a portion of thesource and connecting the armature and exciting winding in series relation across such a portion of the source that the current in the exciting winding is relatively greater for the same armature load current than witlrthe preceding connection and in such a direction that the voltage impressed across the armature is reversed relative to the preceding connection.

15. The method of accelerating an alternating-current conunutator motor of the compensated type having substantially twice as many turns in the compensating winding as in the armature winding, which comprises reversing the direction of the effective voltage in thearmature winding with respect to that in the field windings and simultaneously reducing the voltage across the field windings.

16. The method of accelerating an alternating-current commutator motor of the compensated type having substantially twice as many turns in the compensating winding as in the armature winding, which comprises reversing the direction of the effective voltage in the armature winding withrespect to that in the field windings and simultaneously reducing the voltage across the field windings, and subsequently redlrcing the voltage applied to the compensating field winding while increasing that applied to the arniatu-re and main field windings:

17. The combination with an alternating current motor of the compensated commutator type whereinthe main and com ensating field windings are connected together in series relation and in series with the arma ture winding, theentire motor being connected across a source of alternating current, and the compensating field winding having substantially twice as many turns'as the armature winding, of a connection from the inner terminal of the armaturewinding to a point in said source outside the main motor connections, means for opening said con nection and for short circuiting the armature winding, and means for reestablishing said connection at a point between the main motor connections.

18. The combination with an alternating current motor of the compensated commutator type wherein the main and compensating field windings are connected together in series relation and in series with the armature winding, and wherein the compensating field winding has a greater number of turns than the effective magnetizing turns of the armature winding, the entire motor being connected across a source of alternating current, of a connection from the inner terminal of the armature winding to a point in said source outside the main motor connections, means for opening said connection and for short circuiting the armature winding, and means for reestablishing said connection at a point between the main motor connections.

19. The method of operating an alternatingcurrent commutator motor having a field winding and an armaturewindiing and having a compensating field winding of substantially twice the turns of said armature winding, which consists in connecting said windings in series relation across a portion of said transformer winding and connecting the point common to the armature and the field windingcircuits to a point on said transformer winding, and subsequently reversing the voltage impressed across the armature circuit by connecting said common point to a second point on said transformer winding.

20. In a control system, the combination of a transformer, an alternatingcurrent commutator motor having a cross-field winding and an armature winding, said crossfield winding having substantially twice as many turns as said armature winding, means for connecting said windings to said transformer so that each of said windings constitutes a part of two different electric circuits, both circuits being connected to a common point on said transformer, and means for reversing the voltage impressed upon the circuit containing the armature winding by changing the common point of connection to the transformer without changing the connection of the other terminal of the armature circuit.

21. In a control system, the combination with a transformer, of an alternating-curupon the armature circuit and simultaneously increasing the resultant voltage impressed upon the armature winding by conduction from said transformer and by transformer action in said armature windings from said cross-field winding.

22. The method of operating an alternating'current motor of the compensated commutator type wherein the main and compensating field windings and the armature winding are connected in series relation that consists in connecting the series circuit and said armature winding to predetermined portions of a source of alternating current, temporarily reducing the current in one of said windings, and transferring the intermediate tap from the motor armature terminal to a point intermediate the fieldwindings.

23. The combination with an alternatingcurrent motor of the commutator type having a plurality of field windings connected in series circuit, of a transformer Winding, means for initially connecting different portions of said transformer winding to said series circuit and to the armature winding of said motor, a translating device, means for connecting said translating device to divert a portion of the current from one of said motor windings, means for connecting an intermediate point in said field windings to a predetermined point in said transformer, and means for rendering said device ineffective.

In testimony whereof, I have hereunto subscribed my name this 31st day of Dec. 1913.

RUDOLF E; HELLMUND.

Witnesses:

JOHN S. DEAN, B. B. HINns.

00,! of this patent my be obtlhml for the cent: each, by addressing the Commissioner of Patel,

Wuhln'gtol, D. 0. 1 

